Reciprocal microwave phase shifter



Oct. 12, 1965 F. REGGIA ETAI. 3,212,031

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9 G. H wg m M o EN \VE& 0 F.. 2 @i o Huw LEo M5 WNY am m AR mC. 0 w w. w N o FERm-rs Ron DIAMETER United States Patent O 688,792, Oct. 7, 1961, Ser. No.

2 Claims. (Cl. 333-31) (Granted under Title 35, U.S. Code (1952), sec. 266) This application is a continuation of application, Serial No. 688,792, tiled October 7, 1957, now abandoned.

The invention described herein may be manufactured and used by or for the Government for governmental purposes without the payment to us of any royalty thereon.

This invention relates generally to reciprocal microwave phase shifters, and more particularly to a microwave phase shifter which makes use of a new design technique for obtaining large phase changes per unit length by electrical means.

The prior art has used ferrites with electrically controlled magnetic eld means to produce various types of microwave phase Shifters. The difficulty with these phase Shifters of the prior art is that very large magnetic fields were required to obtain a small amount of phase shift. This invention overcomes the problems of the prior art by means of a new design technique which permits very large reciprocal phase shifts with small applied magnetic fields.

In the prior art, to obtain large phase shifts required very large external control lields of the order of thousands of oersteds, and a complex waveguide system of considerable size. This large size has made the use of these ferrite phase Shifters in microwave systems very impractical. Even using very large fields of many thousands of oersteds, the prior art has found it diicult to obtain phase shifts up to 100 degrees per inch.

This invention makes possible reciprocal phase shifts of greater than 250 degrees per inch with external control fields of only about 50 oersteds and phase shifts greater `than 300 degrees per inch with control elds of about 100 oersteds. These phase shifts are obtainable with variations in transmitted power as low as 0.2 decibel and with insertion losses of less than 0.1 decibel per inch. With such large phase shifts obtainable for low external magnetic control fields, the size of the phase shifter can be very much miniaturized. The electrical characteristics of this phase shifter combined with its geometrical configuration and small size make this electrically controlled ferrite phase shifter very useful in the design of rapid scanning antennas or other microwaves systems requiring phase modulation.

The invention essentially comprises a ferrite rod located inside a nonsymmetrical rectangular waveguide with a longitudinal magnetic field applied to the ferrite rod. As is known in the prior art, if a longitudinal magnetic field is applied to a `ferrite 4rod inside an axially symmetrical waveguide system excited with a linear wave, a rotation of the plane of polarization of the microwave energy occurs. Such a system is non-reciprocal. However, if the ferrite rod is placed within a non-symmetrical 3,212,031 Patented Oct. 12, 1965 ICC rectangular waveguide section, as in the present invention, and the ferrite rod is not too large, this rotational effect will be suppressed and a large phase delay of the microwave energy occurs. The term non-symmetrical rectangular waveguide as used in this application refers to a rectangular waveguide having one of its dimensions below cutoff and the other above cutoi, so that propagation occurs for only one plane of polarization at the fundamental mode. With the ferrite rod centrally located within this waveguide, the ferrite phase shifter will be of the reciprocal type and reversing the direction of the external applied field and/or direction of propagation will give the same phase delay of the microwave energy.

An object of this invention is to provide an improved reciprocal ferrite phase shifter.

Another object is to provide a new design technique for obtaining large phase changes per unit length by electrical means.

Still another object is to provide a microwave ferrite phase shifter which produces large phase shifts with small applied magnetic field.

A further object of this invention is to provide a miniaturized microwave phase shifter.

An additional object is to provide an improved antenna system for obtaining rapid beam scanning of microwave energy by electrical means, using the novel microwave phase shifter of this invention.

The specific nature of the invention, as well as other objects, uses, and advantages thereof, will clearly appear from the following description and from the accompanying drawing, in which:

FIG. l is a schematic and cross-sectional representation of a reciprocal microwaves phase shifter in accordance with the invention.

FIG. 2 is an end view of FIG. l.

FIG. 3 is a graph showing the electrical characteristics of an X-band phase shifter constructed as in FIGS. 1 and 2.

FIG. 4 is a graph showing the effect on the electrical characteristics of a phase shifter constructed as in FIGS. l and 2 when the diameter of the ferrite rod is varied.

FIG. 5 is a schematic and cross-sectional representation of a modified phase shifter in accordance with the invention.

FIG. 6 is an end view of FIG. 5.

FIG. 7 is a graph showing the electrical characteristics of an X-band phase shifter constructed as in FIGS. 5 and 6.

FIG. 8 is a graph showing the bandwidth characteristics of the X-band phase shifter constructed as in FIGS. 5 and 6.

FIG. 9 is a graph showing the guide wavelength vs. the diameter of the ferrite rod of the X-band phase shifter constructed as in FIGS. l and 2.

FIG. l0 is a schematic and cross-sectional representation of a microwave antenna system for electrical beam scanning in accordance with the invention.

In FIGS. l and 2, a non-symmetrical rectangular waveguide section 10 adapted to be excited in the TEN mode has a ferrite rod 12 centrally located within the section 1li. Supporting means 15 are used to centrally support the ferrite rod 12 within the waveguide section 10. Dielectric matching elements 17, having the same diameter as the ferrite rod 12, are affixed to both ends of the ferrite rod 12 to provide impedance matching. A longitudinal magnetic field H is produced within the rod 12 by the solenoid means 19 through which a current I flows. In the operation of the phase shifter of FIGS. l and 2, microwave energy is applied to one end of the waveguide section 10. After passing through the waveguide 10, the microwave energy received at the output end will be delayed in phase by an amount dependent upon the magnitude of the magnetic field H and the geometrical characteristics of the ferrite rod 12. It is important that the diameter of the rod be sufficiently small so as to substantially suppress rotation of the plane of polarization of microwave energy propagated through the non-symmetrical rectangular waveguide section 10. It is also irnportant that the rectangular waveguide section 10 be nonsymmetrical so that propagation occurs only for one plane of polarization.

FIG. 3 is a graph showing the electrical characteristics of a particular Xband reciprocal phase shifter constructed as in FIGS. l and 2. This X-band pha-se shifter cornprises a non-symmetrical rectangular X-band waveguide section 10 having a centrally located round ferrite rod 12. The ferrite rod 12 is 4 inches long, has a diameter d of 0.3 inch, and is made of a commercially available low-loss MgMn ferrite such as General Ceramics Corporation R-'l ferrite. A single Teflon support 15, 3/16 `inch long, was used to centrally locate the ferrite rod 12 in the X-band waveguide section 10. A 0.3 inch length of Stycast dielectric 17 having the same diameter as the 'power no greater than plus or minus 0.7 db were obtained. It is interesting to note that most of the phase shift obtained occurred for magnetic fields less than 100 oersteds. The insertion loss of this phase shifter was approximately 0.3 db and a D.C. power of 5 watts was required to obtain a field strength of 100 oersteds.

FIG. 4 shows the effect on the electrical characteristics of a phase shifter constructed as in FIGS. l and 2 when fthe diameter of the ferrite rod 12 is varied. -For these measurements the X-band phase shifter described in connection with FIG. 3 was used with several 4-inch long round ferrite rods of different diameters. It can be seen from FIG. 4 that small phase shifts are obtained for rod diameters less than 0.225 inch. Increasing the rod diameter above this figure results in large phase shifts, most of which occurs for fields less than 60 oersteds. For diameters greater than 0.30 inch, little increase in phase shift is obtained and" large changes in the transmitted power and the VSWR (not shown in the figure) begin to occur. At X-band frequencies, therefore, where the ferrite rod is made from MgMn, the diameter of lche ferrite rod 12 should preferably be between 0.20 and 0.30 inch.

FIGS. 5 and 6 show a modified and improved form of vthe phase shifter of FIGS. l and 2. A square ferrite rod 13 tapered at the ends 18 for matching purposes is used instead of the round ferrite rod 12 and the matching elements 17 of FIGS. l and 2. This construction results in considerably better impedance matching and greater phase shifts, and also allows the phase shifter to operate over a larger frequency range. FIGS. 5 and 6 also show novel means for obtaining the longitudinal magnetic field H. Two low-current solenoids 20 and 21 are mounted on opposite sides of the waveguide section 10, with current I flowing through them so as to produce opposing fields which add in parallel along the length of the ferrite rod 30. The symbols N and S indicate the polarities 4 of the solenoids 20 and 21 for which this adding of fields is obtained. Solenoids such as 20 and 21 are commercially available and may be used to produce a longitudinal magnetic field within a standard waveguide section without the need for special modifications in construction.

FIG. 7 is a graph showing the electrical characteristics of a particular X-band phase shifter constructed as in FIGS. 5 and 6. This X-band phase shifter comprises a non-symmetrical rectangular S-band waveguide section 10 having a centrally located square ferrite rod 13 tapered at its ends 18. The ferrite rod 13 is 4 inches long, has a diameter d of 0.3 inch, and is made of commercially available low-loss MgMn ferrite, such as General Ceramics Corp. R-l ferrite. The tapered ends 18 are 2A; inch in length. A single polyfoam support 15, 3/16 inch long, was used to centrally locate the ferrite rod 12 in the X-band waveguide section 10. The solenoids 20 and 21 are two commercially available low-current solenoids 21/2 inches long and are mounted on the waveguide section 10. The variation in transmitted power is approximately plus or minus 0.1 decibel throughout the range from 0-1200 degrees phase shift and the insertion loss is approximately 0.6 decibel. Approximately 1.0 watt of D.C. power is required to obtain a magnetic field strength of 50 oersteds.

A comparison of the graphs of FIGS. 3 and 7 indicates that an improvement in electrical characteristics is obtained for the X-band phase shifter constructed as in FIGS. 5 and 6. Improvement in bandwidth is also obtained by this improved phase shifter. FIG. 8 is a graph showing the large bandwidth that is obtained for the X-band phase shifter constructed as described in connection with FIG. 7.

FIG. 9 is a graph showing the change of guide wavelength (kg) at 9100 mc. vs. the diameter d of the round ferrite rod 12 used in the phase shifter as constructed in FIGS. l and 2. Starting with kg equal to 4.75 for the empty waveguide, it i-s seen that little change in guide wavelength Ag occurs for rod diameters up to approximately 0.15 inch. However, for diameters greater than this, a rapid decrease in Ag occurs, reaching a figure of 1.86 cm. for a rod diameter of 0.30 inch. It also has been observed that the field within the waveguide section 10 is redistributed by the ferrite rods so that the microwave energy is concentrated towards the center of lthe waveguide section 10. Knowing the field distribution within the guide and the guide wavelength Ag, those skilled in the art will be able to design various types of miniature antenna systems in accordance with the invention.

Measurements on ferrite rods up to 8 inches in length have shown that the magnitude of the phase shift obtained is directly proportional to the length of the ferrite rod 12. Therefore, the units of degrees per inch may advantageously be used as the unit of phase shift in the phase shifter of this invention. In FIG. 3, for example, an applied field H of 60 oersteds produces a phase shift of 250 degrees per inch, and an applied field H of 60 oersteds in FIG. 7 produces a phase shift of 290 degrees per inch. This unit of phase shift is especially meaningful where the phase shifter is used for beam scanning long linear arrays excited from a rectangular waveguide section.

FIG. l0 is an example of one type of improved antenna system which may be constructed in accordance with the invention. In FIG. 10 a rectangular waveguide section 10 is excited with microwave energy at its input. Radiating elements 30 are placed at suitable points along the waveguide 10 so as to radiate power out of the waveguide. A ferrite rod element, made up of ferrite sections 13a, 13b and 13C, is supported at the center of the waveguide 10 by supporting elements 15a, 15b and 15C. The ferrite rod elements 13a, 13b and 13C can be made up in convenient length and readily joined together by pressure contact with little effect upon performance. The radiating elements 30 may be slots instead of dielectric rods, it` so desired. The direction of maximum radiation of the fan-shaped beam depends upon the guide wavelength Ag which decreases when a longitudinal magnetic field H is applied. Any suitable means, such as shown in FIGS. 1 and 2 and FIGS. 5 and 6 can be used to produce the longitudinal magnetic field H. A change in the applied magnetic lield H produces a phase shift which introduces a progressive delay in the wave front down the waveguide, thus causing the radiated wave front to sweep over the scanning sector.

Although X-band operation has been used in particular illustrations of the invention, it should be understood that this invention may also be applied to other frequency regions.

It will be apparent that the embodiments shown are only exemplary and that various modifications can be made in construction and arrangement within the scope of the invention as defined in the appended claims.

We claim as our invention:

1. A low insertion loss, reciprocal microwave phase shifter which produces large phase changes per unit length while substantially suppressing amplitude modulation of microwave energy comprising:

(a) a rectangular waveguide section having crosssectional dimensions which permit propagation in only one plane of polarization at the fundamental mode,

(b) a ferrite rod centrally located within said waveguide section, and

(c) means for applying a longitudinal magnetic field having a value between zero biasing and saturation to said ferrite rod, said ferrite rod having crosssectional dimensions large enough to permit substantial concentration of the microwave energy in the rod but smaller than that which will permit Faraday rotation at said value of the longitudinal magnetic eld.

2. A low insertion loss, reciprocal microwave phase shifter as recited in claim 1 wherein:

(a) said rectangular waveguide section is an X-band waveguide section;

(b) said ferrite rod is made of a low-loss MgMn ferferrite and has a diameter between 0.20l and 0.30 inch; and

(c) the strength of the magnetic field produced by said means for applying a longitudinal magnetic field is less than 100 oersteds.

References Cited by the Examiner UNITED STATES PATENTS 8/57 Read 333-24.2 1/62 Sferrazza 333--98 OTHER REFERENCES ELI LIEBERMAN, Primary Examiner.

HERMAN KARL SAALBACH, Examiner. 

1. A LOW INSERTER LOSS, RECIPROCAL MICROWAVE PHASE SHIFTER WHICH PRODUCES LARGE PHASE CHANGES PER UNIT LENGTH WHILE SUBSTANTIALLY SUPPRESSING AMPLITUDE MODULATION OF MICROWAVE ENERGY COMPRISING: (A) A RECTANGULAR WAVEGUIDE SECTION HAVING CROSSSECTIONAL DIMENSIONS WHICH PERMIT PROPAGATION IN ONLY ONE PLANE OF POLARIZATION AT THE FUNDAMENTAL MODE, (B) A FERRITE ROD CENTRALLY LOCATED WITHIN SAID WAVEGUIDE SECTION, AND (C) MEANS FOR APPLYING A LONGITUDINAL MAGNETIC FIELD HAVING A VALUE BETWEEN ZERO BIASING AND SATURATION TO SAID FERRITE ROD, SAI FERRITE ROD HAVING CROSSSECTIONAL DIMENSIONS LARGE ENOUGH TO PERMIT SUBSTANTIAL CONCENTRATION OF THE MICROWAVE ENERGY IN THE ROD BUT SMALLER THAN THAT WHICH WILL PERMIT FARADAY ROTATION AT SAID VALUE OF THE LONGITUDINAL MAGNETIC FIELD. 